Field
The present invention relates to a non-aqueous electrolyte for a lithium secondary battery including a dinitrile-based additive to improve the cycle life and suppress swelling, and a lithium secondary battery comprising the same.
Description of Related Art
Recently, there is an increasing interest in energy storage technologies. As the application fields of energy storage technologies have been extended to mobile phones, camcorders, lap-top computers, and even electric cars, the demand for high energy density of batteries used as power sources of electronic equipment has been increasing. Lithium secondary batteries are given attention as the most favorable battery capable of meeting the demand, and currently studies are being actively made on lithium secondary batteries.
Lithium secondary batteries developed in the early 1990's are made up of an anode of a carbon-based material capable of intercalating and deintercalating lithium ions, a cathode of lithium containing oxide, and a non-aqueous electrolyte containing a proper amount of lithium salts dissolved in a mixed organic solvent.
Recently, with the expanded use of lithium secondary batteries, there is an increasing demand for lithium secondary batteries capable of safely charging in extreme conditions, such as high or low temperature and high voltage conditions, while maintaining excellent performance.
Lithium secondary batteries use, as a cathode active material, lithium transition metal oxide or composite oxide of which the structural stability and the capacity are determined by the intercalation and deintercalation of lithium ions, and the capacity increases with the increasing charge potential, which accelerates the discharge of transition metal constituting the active material, resulting in structural instability.
At present, an organic solvent widely used in a non-aqueous electrolyte includes ethylene carbonate, propylene carbonate, dimethoxy ethane, γ-buryrolactone, N,N-dimethylformamide, tetrahydrofuran, acetonitile, and the like. However, when these organic solvents are stored at high temperature for a long time, batteries may deteriorate due to gas generated by electrolyte oxidation and consequently swelling. In this instance, the generated decomposition gas deforms a pouch-shaped electrode assembly or a cylindrical or prismatic electrode assembly, resulting in internal short circuit. In severe cases, ignition or explosion of batteries may occur. The electrolyte oxidation may be accelerated by the elution of transition metal under high voltage conditions.
To solve these problems, a variety of additives used in a non-aqueous electrolyte have been suggested to prevent batteries from swelling, however to date, there is no effective solution. For example, when succinonitrile is added to an electrolyte, swelling may be suppressed to some extent but charge/discharge cycle life reduces.